This invention relates generally to vibration damping in support structures, and more particularly the invention relates to a loading mechanism and a support structure having improved vibration damping especially useful in scanning tunneling microscopy.
The scanning tunneling microscope as introduced by Binnig et al. has proved to be a great tool for surface science as it can provide images which indicate the positions of individual atoms in real space. The microscope includes a vacuum chamber in which a support is provided for mounting a body having a surface to be examined. A very sharp tungsten-tipped electrode is brought into close contact with the surface. The electrode is biased with an appropriate tunneling voltage, and the distance between the electrode tip and the surface is indicated by the tunnel current flowing between the electrode and the surface. The electrode is mounted on a scanner consisting of three orthogonal piezoelectric bars. The scanner moves the tip with atomic precision along the three axes. The conducting specimen under study is mounted on the translation stage, and the sample is moved toward the tip until the gap between the tip and the sample becomes small enough for quantum mechanical tunneling to occur. The tunneling current is exponentially proportionate to the gap spacing, and, therefore, is very sensitive to changes in gap spacing. A feedback system detects the tunneling current and drives the vertical axis (Z) of the scanner so that the gap spacing is maintained at a constant value. Raster scanning is performed on the other axes (X, Y) while a computer records the displacement of the Z axis as a datum at each X, Y position. This two-dimensional data represents the geometry of the sample surface under the assumption that the constant work function and local density of states of the sample are both constant during the time of single image.
While the principle behind scanning tunneling microscopy is simple, many critical design considerations need to be solved in order to achieve atomic resolution. One such design consideration is the mounting of the specimen to minimize vibrations during movement of the electrode. Currently, two vibration isolation systems are used in scanning tunneling microscopy. The first on is a single coil spring suspension with magnetic damping, and the second is a stack of stainless-steel plates with Vitron dampers between each pair of plates. While both systems have been used in scanning tunneling microscopy instruments capable of recording images with atomic resolution, the second system is easy to build and relatively rigid so that it is convenient to manipulate the internal components. On the other hand, the system needs additional pneumatic suspension to improve the vibration isolation at low frequencies.